TAP-GRIN: Interventional Study on Patients With GRIN-related Neurodevelopmental Disorders

Summary

The goal of this clinical study is to find out whether L-serine dietary supplementation helps improve overall clinical functioning in children and young adults (2-30 years) with GRIN-related neurodevelopmental disorders (GRIN-NDD) caused by loss-of-function (LoF) variants in GRIN1, GRIN2A, GRIN2B, or GRIN2D. It will also assess the safety and tolerability of L-serine.

The main questions it aims to answer are:

Does L-serine improve overall clinical status, measured mainly by the Clinical Global Impression-Severity (CGI-S) score?

Does L-serine improve behaviour, cognition, adaptive functioning, motor skills, sleep, and (in those with epilepsy) seizure frequency and EEG findings?

What side effects or medical problems occur during L-serine compared with placebo?

Do neurophysiological measures (including TMS-EMG/TMS-EEG) change with treatment and potentially act as biomarkers of response?

Researchers will compare L-serine to a placebo (maltodextrin powder with similar appearance/texture) using a randomised, double-blind, placebo-controlled "n-of-1" approach, where each participant receives both treatments in alternating periods. Results from multiple single-patient trials will then be combined (aggregated) to estimate the overall treatment effect across the study population.

Participants will:

Complete a 4-week baseline period with assessments (and seizure diary use where applicable)

Receive L-serine and placebo in alternating 3-month periods within each cycle (minimum 2 cycles, up to 4 cycles; each cycle lasts 6 months)

Take the assigned study product by mouth 3 times per day at 500 mg/kg/day (maximum 30 g/day for participants ≥60 kg)

Have the first 7 days of each 3-month period treated as washout, with data from that week not analysed

Attend regular clinic visits for clinical exams, safety labs, and standardized assessments of global status, behaviour/cognition, motor function, and sleep

If they have epilepsy: keep a seizure diary and undergo EEG assessments after each treatment period

In some sites (Italy and France): undergo TMS-based neurophysiology testing

Optionally, a subset may join a cellular biomarker substudy (blood collection to generate iPSC-derived neuronal models and organoids) to explore treatment effects in variant-specific lab models.

Conditions

• GRIN-related Disorders
• GRIN1
• GRIN2A
• GRIN2B
• GRIN2D
• Epilepsy
• Neurodevelopmental Disorder (Diagnosis)

Interventions

DIETARY_SUPPLEMENT

L-serine

L-serine supplementation is administered as an oral powder for solution and used as an add-on intervention to participants' existing standard of care. L-serine is a naturally occurring amino acid and is classified as a food for special medical purposes. In this study, L-serine is used to increase the availability of its enantiomer D-serine, an endogenous co-agonist of the N-methyl-D-aspartate receptor (NMDAR), with the aim of enhancing NMDAR-mediated neurotransmission in individuals with GRIN-related neurodevelopmental disorders caused by loss-of-function variants. The intervention is delivered using a randomised, double-blind, placebo-controlled n-of-1 design, in which each participant receives both L-serine and placebo in alternating treatment periods. L-serine and placebo are identical in appearance, packaging, and method of administration to maintain blinding. Treatment allocation within each cycle is determined by a computer-generated randomisation schedule managed by unblinded s

OTHER

Maltodextrin (Placebo)

Placebo is administered as an oral powder for solution and serves as the comparator to L-serine supplementation. The placebo consists primarily of maltodextrin, a readily digestible carbohydrate that is commonly used as an inert control substance in clinical studies. It is classified as a food-grade product and contains no active amino acids or pharmacologically active ingredients. The placebo is formulated to be indistinguishable from L-serine with respect to appearance, texture, solubility, and method of administration, in order to maintain blinding of participants, caregivers, investigators, and study staff. Packaging, labelling, and dosing instructions are identical to those used for the active intervention. The placebo is administered orally in three divided daily doses, following the same dosing schedule and duration as the active intervention within the randomised, double-blind, n-of-1 trial design. Each placebo treatment period lasts three months, with the first seven days de

Sponsors & Collaborators

• Meyer Children's Hospital IRCCS

  lead OTHER

Study Design

Allocation

RANDOMIZED

Purpose

TREATMENT

Masking

QUADRUPLE

Model

CROSSOVER

Eligibility

Min Age

2 Years

Max Age

30 Years

Sex

ALL

Healthy Volunteers

No

Timeline & Regulatory

Start

2025-08-29

Primary Completion

2028-06-30

Completion

2028-06-30

Countries

• France
• Italy
• Poland

Study Locations